The Republican-led lower chamber of US Congress passed a $14 billion aid package for Israel on Thursday, defying President Joe Biden's request to also include more money for Ukraine and other pressing priorities.

The bill, which diverts funding budgeted to the US tax collection agency, is almost certain to fail in the Democratic-controlled Senate, while Biden has also threatened to veto it.

The White House has requested a larger, multifaceted package of support for both Israel and Ukraine, as well as humanitarian aid for Gaza and additional funding for US border-related projects.

But debate over the key issues is just beginning in earnest after a weeks-long delay while House Republicans struggled to name a new speaker, and it is unclear what, if anything, can get through both chambers.

Both Democrats and Republicans in Congress want to promptly adopt military aid for Israel, a long-standing US partner at war with Hamas.

Things get more complicated, however, when it comes to Ukraine.

Washington is Kyiv's biggest military backer, having committed tens of billions of dollars since Russia invaded in February 2022.

But Biden's pledge of uninterrupted financial support reiterated during Ukrainian President Volodymyr Zelensky's visit to Washington in September, looks to be in jeopardy.

$106 billion request

In the House of Representatives, where Republicans hold a slim majority, a few hard-line conservatives have demanded an immediate end to Ukraine funding.

The chamber is only just emerging from an unprecedented three-week paralysis after the previous Republican speaker was ousted in a rebellion by the same hard-line group.

The situation is drastically different in the Democrat-controlled Senate, where most Republicans have voiced support for boosting aid to Ukraine.